Diamonds have excellent characteristics such as high light transmissivity, high thermal conductivity, high carrier mobility, high dielectric breakdown electric field and low inductive loss, and are widely used for cutting tools and abrasion-proof tools particularly because of its unusually high hardness. Heretofore, a natural single-crystal diamond or a single-crystal diamond synthesized by a high-temperature and high-pressure method has been widely used, but in recent years, it has been possible to synthesize a thick and self-standing single-crystal diamond even by a chemical vapor deposition method, and application of such a single-crystal diamond in various fields as described above has been expected.
Studies have been extensively conducted on improvement of quality of a CVD (chemical vapor deposition) single-crystal diamond as described above. For example, in Proceedings of Japan Society of Applied Physics Academic Meeting in Spring, 2004, page 635 (NPD 1), a distribution of defects such as dislocations is observed by X-ray topography of a homoepitaxial diamond obtained by a CVD (chemical vapor deposition) method. In addition, National Patent Publication No. 2004-503461 (PTD 1) discloses a method in which the density of defects on a surface of a diamond base as a seed substrate is reduced, and a diamond is then synthesized by a CVD method for obtaining a CVD single-crystal diamond having light transmissivity and excellent electronic physical properties with regard to a high-quality CVD single-crystal diamond layer having a thickness greater than 2 mm, and a method for production thereof.